The study of morphogenesis during the developmental stage has been conducted based on the screening of variant using Drosophila. Hedgehog gene (hh) was found as one of the genes that cause morphological abnormality of Drosophila embryo due to mutation thereof. Hedgehog gene product (Hh) is a secretory protein, which is produced as an about 45 kDa precursor and then divided, due to autolysis, into a 20 kDa N-terminal side domain, which is a main active principle, and a 25 kDa C-terminal side domain. The 20 kDa N-terminal side domain, which is a main active principle, is modified by fatty acid on the N-terminal and cholesterol on the C-terminal thereof. The Hedgehog signal transduction system is formed by the protein group described below. Hh receptor is Patched (Ptch), which is a twelve-transmembrane-type protein. Ptch acts on Smoothened (Smo), which is a seven-transmembrane-type protein, and suppresses the function of Smo in the absence of Hh. When Hh is bound to the receptor Ptch, suppression of Smo is released and Smo is activated. The signal produced by the activation of Smo activates transcription factor Ci, which regulates the expression of the gene group involved in the morphogenesis (Curr. Opin. Genet. Dev., vol. 12, pages 503-511, 2002).
A pathway corresponding to the Drosophila Hedgehog signal transduction system has been confirmed also in mammals. In human, for example, three types of gene products, sonic hedgehog (Shh), indian hedgehog (Ihh) and desert hedgehog (Dhh), are known to correspond to Drosophila Hh, and undergo post-translational modification as in Drosophila Hh (Cell, vol. 103, pages 371-374, 2000). In human Shh, a 19 kDa active principle is cleaved out from a 45 kDa precursor protein by autolysis, and fatty acid is added to the N-terminal thereof, and cholesterol is added to the C-terminal thereof (J. Biol. Chem., vol. 273, pages 14037-14045, 1998). Such modification is considered to be essential for the maintenance of Shh activity and, for example, 40 times enhanced activity was achieved by the addition of palmitic acid to Escherichia coli recombinant human Shh free of N-terminal modification with fatty acid, and 160 times enhanced activity was achieved by the addition of myristic acid thereto (Biochemistry, vol. 40, pages 4359-4371, 2001). On the other hand, as a human gene corresponding to Drosophila Smo, human Smo is known, and as a human gene corresponding to Drosophila Ptch, 2 types of Ptch1 and Ptch2 are known. In addition, a transcription factor corresponding to Drosophila Ci is considered to be Gli in human, and 3 types of Gli1, Gli2 and Gli3 are known (Nature Rev. Cancer, vol. 2, pages 361-372, 2002). Shh/Ihh/Dhh are each bound to Ptch1 and activate Smo by inhibiting the bond between Ptch1 and Smo. Shh/Ihh/Dhh are also bound to Ptch2, Hip1, Gas1 and Cdo/Boc, besides Ptch1, and regulate the activation of Smo. A signal transduction from Smo induces nuclear localization of Gli1 and Gli2, and activate transcription of Gli1 (Curr. Opin. Cell Biol., vol. 19, pages 159-165, 2007).
The Hedgehog signal is involved in the morphogenesis in the developmental stages also in mammals. In human, for example, patients with Holoprosencephaly, which is a congenital developmental abnormality, showed mutation in Shh (Nat. Genet., vol. 14, pages 357-360, 1996). Moreover, a natural compound Cyclopamine derived from white hellebore known as a compound inducing Cyclopus in sheep (Am. J. Vet. Res., vol. 24, pages 1164-1175, 1963) was confirmed to inhibit Smo as action mechanism thereof (Development, vol. 125, pages 3553-3562, 1998). Furthermore, an Shh knockout mouse was prepared, and its phenotype was found to include Cyclopus, malformation of extremities (Nature, vol. 383, pages 407-413, 1996), and neural plate malformation (Cell, vol. 111, pages 63-75, 2002).
Hedgehog signal is inherently a developmental signal, which is promoted in tumor tissues and functions as a cancer cell proliferation and survival signal. Hedgehog signal is considered to function for the growth and survival of cancer cells in an autocrine mode, or function between cancer cells and cancer interstitial cells in a paracrine mode, in tumor tissues (Nat. Rev. Drug Discov., vol. 5, pages 1026-1033, 2006). In an autocrine mode, it works for the growth and maintenance of cancer cells, via transcription activation by Gli-1, by abnormal cell cycle control due to increased expression of Cyclin D and decreased expression of p21, promotion of proliferation signal by activation of EGFR pathway and the like. On the other hand, since Shh expressed in cancer cells acts on Smo in cancer interstitial cells, growth factors such as insulin-like growth factor-1, fibroblast growth factor, platelet-derived growth factor and the like are transmitted from cancer interstitial cells to cancer cells, and function for the growth and survival of cancer cells. It is also considered that promotion of VEGF, PDGF pathway and the like by Gli-1 promotes tumor angiogenesis (Clin Cancer Res., vol. 12, pages 5924-5928, 2006). As to the mechanism of promotion of Hedgehog signal, a cancer in which Hedgehog signal is promoted due to mutation of Ptch1 and a cancer which is promoted by overexpression of Shh, which is one of the ligands, have been reported (Nature Rev. Cancer, vol. 3, pages 903-911, 2003). As a cancer in which Hedgehog signal is promoted due to mutation, basal cell cancer and medulloblastoma are known, and mutation of Ptch1 observed in these cancers activates Hedgehog signal in a ligand independent manner (Am. J. Med. Gen., vol. 123A, pages 5-28, 2003). As a cancer in which Hedgehog signal is promoted by overexpression of Shh, pancreatic cancer (Nature, vol. 425, pages 846-851, 2003) and the like have been reported. In a transgenic mouse in which Shh is forcedly expressed in the pancreas, Hedgehog signal is suggested to be involved not only in the growth and maintenance of cancer, but also carcinogenic process, since a PanIN-like lesion in the initial stages of cancer progress was found in the pancreas (Nature, vol. 425, pages 851-856, 2003). Furthermore, Hedgehog signal is considered to function for the growth and survival of cancer stem cells, and play a key role in the metastasis or postoperative recurrence of tumor and the like (Trends Cell Biol., vol. 17, pages 438-447, 2007).
As the Hedgehog signal inhibitor, the following are known. Cyclopamine, which is a naturally occurring Smo inhibitory compound, has been reported to show a tumor growth suppressive effect on glioma (Development, vol. 128, pages 5201-5212, 2001) and the like. As a synthetic low-molecular-weight compound inhibiting Smo, CUR-61414 (Proc. Natl. Acad. Sci. U.S.A., vol. 100, pages 4616-4621, 2003) and SANT-1, 2, 3, 4 (Proc. Natl. Acad. Sci. U.S.A., vol. 99, pages 14071-14076, 2002) have been reported. As for the Hedgohog signal inhibitory antibody, it has been reported that administration of an anti-Shh antibody to a cancer-carrying nude mouse transplanted with colorectal cancer cell line HT-29 caused regression of cancer (WO 2004/020599).
Patent documents 1 to 5 disclose fused heterocycle compounds.